Fig. 1. Polarization-sensitive absorption of graphene under TIR condition. (a) Sandwich structure model with graphene under TIR condition; (b) relationship between the reflectance at TE/TM polarization states and the incident angle with graphene under TIR condition; (c) relationship between the reflectance difference and the refractive index of the optically thinner medium with/without graphene

Fig. 2. Schematic diagram of graphene-based optical biosensor

Fig. 3. Flowchart of refractive index sensing for functionalized magnetic nanoparticles

Fig. 4. Modification of Fe₃O₄@Au magnetic nanoparticles. (a) TEM image of Fe₃O₄@Au nanoparticles; (b) UV-visible spectrum of Fe₃O₄@Au nanoparticles

Fig. 5. Voltage response of refractive index at different sodium chloride concentrations. (a) Real-time voltage change; (b) relationship of refractive index and voltage

Fig. 6. Real-time voltage response when magnetic nanoparticles was immobilized on the surface of graphene

Fig. 7. Bright-field micrograph of magnetic nanoparticles adsorbed on the surface of graphene under different magnetic field intensities. (a) 0 mT; (b) 80 mT

Fig. 8. Real-time voltage response of Ochratoxin A at different concentrations

Fig. 9. Relationship between different concentrations of Ochratoxin A and output voltage

Fig. 10. Comparison of voltage response of aflatoxin B₁ and ochratoxin A